This is similar to <a href="/p/project-zero/issues/detail?id=1531" title="Microsoft Edge: Chakra: JIT: Magic value can cause type confusion" class="closed_ref" rel="nofollow"> issue 1531 </a>. The patch seems to prevent type confusion triggered from StElemI_A instructions. But the SetItem method can also be invoked through the Array.prototype.push method which can be inlineed. We can achieve type confusion with the push method in the same way used for <a href="/p/project-zero/issues/detail?id=1531" title="Microsoft Edge: Chakra: JIT: Magic value can cause type confusion" class="closed_ref" rel="nofollow"> issue 1531 </a>.